DOCX Input: if no language is defined in the metadata, use the language specified in the document default style. Fixes #1321346 [DOCX Input language detection](https://bugs.launchpad.net/calibre/+bug/1321346)

src/calibre/ebooks/docx/container.py

@@ -71,6 +71,14 @@ def read_app_props(raw, mi):
     company = root.xpath('//*[local-name()="Company"]')
     if company and company[0].text and company[0].text.strip():
         mi.publisher = company[0].text.strip()
+
+def read_default_style_language(raw, mi):
+    root = fromstring(raw)
+    for lang in XPath('/w:styles/w:docDefaults/w:rPrDefault/w:rPr/w:lang/@w:val')(root):
+        lang = canonicalize_lang(lang)
+        if lang:
+            mi.languages = [lang]
+            break
 # }}}
 
 class DOCX(object):
@@ -207,6 +215,13 @@ class DOCX(object):
                 pass
             else:
                 read_doc_props(raw, mi)
+        if mi.is_null('language'):
+            try:
+                raw = self.read('word/styles.xml')
+            except KeyError:
+                pass
+            else:
+                read_default_style_language(raw, mi)
 
         name = self.relationships.get(APPPROPS, None)
         if name is None: